$wgMediaViewerEnableByDefault and $wgMediaViewerEnableByDefaultForAnonymous will determine whether MMV is enabled by default for everyone and for anonymous users, respectively. They both default to true. $wgDefaultUserOptions['multimediaviewer-enable'] = 1; can be used as a replacement for $wgMediaViewerEnableByDefault.

$wgMediaViewerUseThumbnailGuessing will improve performance when enabled, but can be fragile depending on how the wiki is set up (it will probably work fine if you use a 404 handler).

Forced download

To ensure files are offered for download and not viewed in the user's browser following a click on the Download … button, the server has to be configured, except when using vagrant:

Как пользоваться расширением

First thing, before testing, is to make sure you're logged in and you have the preference enabled: Log in to the wiki and go to Special:Preferences, then visit the "Beta features" tab and check the appropriate box.

Next, go to a page that has a thumbnail on it. Try clicking on the image or on the "expand" icon near it. The lightbox should pop up and give you a bigger view of the image.

If you'd prefer, there's an exported test environment that you can use via Special:Import to quickly set up a suitable testing environment.

Extending with user scripts

If you want to add functionality, you'll have to dig around in the classes and change the functionality pretty manually. We'll work on making this a nicer experience, but given the class and method hierarchy we've built, we think it's not terribly difficult right now.

HOWEVER, you should avoid doing this too much. If things change internally, then your code might break in unexpected ways, and you (and your users) will be surprised. Don't let that happen, and wait for a more stable way to extend the product.